Maleinized polybutadiene, maleinized drying oils, their half esters and half amides have been most widely used as a resin component of electrodeposition paints because of their higher stability in electrodeposition coating bath. However, they have certain disadvantages. They exhibit relatively low anticorrosive effect on iron-based substrates and require relatively high baking temperatures.
The anticorrosive property may be improved by combining with a water-soluble epoxy resin such as epoxy resin fatty acid esters. This, however, greatly decreases the stability of resinous components in the electrodeposition coating bath. Numerous attempts have been made to compensate the above disadvantages of maleinized polybutadiene, maleinized oils, their half esters and half amides. See, Japanese Patent Publication Nos. 21691/72 and 4058/74, for example.
Despite these and other attempts, the prior art paint compositions of the above type failed to meet all of the conditions of cold-curability, anti-salt spraying and bath stability. Accordingly, there exists strong need for a water-based paint composition of the above type which may satisfy all of the above conditions.